Eternal War: Shadows of Light is a Christian based, first person shooter game created by Two Guys Software. Taken from the TGS site:

"Time to stop the Nightmare... Eternal War: Shadows of Light. If you think this a walk in the park, you're wrong. Journey into the dark past of John Coronado, a desperate teen ready to take desperate measures to escape his "personal hell". Explore deep into a deadly stronghold, outsmarting compelling puzzles, putting the smack down on deadly adversaries bent on stopping you. With eight high powered weapons with alternative firing modes it is your turn to turn the tide. If that isn't enough, hook up with your friends and work together in two frantic cooperative multiplayer modes. Failure is not an option. It's time to kick some demon scales."

Quake-based game with models borrowed (with permission) from Quake 2 mod Dawn of Darkness. Included source code.